for more let's brink in jim walsh, an expert at mit securities program. thank you for joining us. >> happy to be here. >> john: i know this has been a day fills with lots of irresponsible speculation so i thank you in advance for any guesswork you may be able to offer us. but can you tell us what kind of explosive device was used? >> it's less than military grade. it's not c-4 or a military grade explosive. the explosive itself, the bomb sat low in the container so much of the damage when it was released under cut people and possibly in the case of one of the fatalities, a child who would have been lower to the ground. but you know, we'll know a lot more in 24 hours. i take your caution here that we should be careful. we've already had a couple of reports i that's to be expected, in part fueled by comments made by the boston police, which is understandable because things are confusing at first. there was a report that the john f. kennedy president presidential library was part of it. the jfk library is some distance from the initial explosion. turns out t